The noise level of jet engines, particularly during takeoff and climb, is in the range of 100 to 110 decibels (dB), and is often a concern for people living near airports. Recent advances in technology in the so-called "high speed civil transport" (HSCT) jets have developed plans for airplanes that surpass the Concorde in size and speed, carrying on the order of 350 to 400 passengers a distance on the order of 6,000 miles at speeds in the vicinity of Mach 2. However, the viability of such planes is presently severely restricted due, not so much to the noise of flying at Mach 2 (the flight patterns are intended to be over water), but rather the noise generated during takeoff and climb.
The noise is particularly exacerbated for HSCT craft, because the engines propelling them cannot have a large amount of by-pass air as is the practice in the current subsonic aircraft.
Various approaches have been used or proposed to overcome the noise problem. Earlier solutions have proposed so-called "daisy" nozzles or tubular nozzles to break up the jet in an effort to reduce noise. More recently, an "ejector-suppressor" has been proposed, comprising a "shroud-like" device which is acoustically lined to reduce noise during takeoff. However, this approach may add as much as 5,000 pounds per engine to the weight of the airplane and increase its drag in addition. This weight is simply dead weight, and results in a loss of thrust by the engine and an increase in drag of the airframe.
A noise suppressor for jet engines, particularly for use on HSCT craft, is required. Such a noise suppressor should not add significant weight to the craft nor adversely affect thrust during cruise.